1. Field of the Invention
This invention is in the field of photosensitive elements which operate by charge separation in a molecular array and transport of electrons and electron holes out of the array. Such elements have use in devices such as photodiodes, photoconductors, and photovoltaic cells for converting incident energy, such as solar energy, to electricity, and to drive electrochemical reactions.
2. Prior Art
In recent years much attention has been given to the development of photosensitive elements, particularly those intended to convert solar energy to electricity. The mechanism of operation of such devices is well understood as outlined, for example, by Butler et al in Journal of Materials Science 15 1-19 (1980). Fundamental to the functioning of such devices is, as is well understood, the radiant energy-induced separation of charges within a molecular or atomic array and charge transport out of the array, for example, to external electrodes or to an electrolyte there to drive an electrochemical reaction, usually a redox reaction.
The literature of photosensitive elements, particularly those employing inorganic materials is voluminous. Recently increasing attention has been given to photosensitive elements employing organic materials such as those of the instant invention. Tang in U.S. Pat. No. 4,164,431, hereby incorporated by reference, provides an excellent review of the state of the art of such elements.
It is generally agreed that efficiency in charge separation and transport out of the array depends on the selection of the materials of the array on the one hand, and on the arrangement of the molecules of the materials within the array on the other.
Materials are selected inter alia so as to provide a so-called spectral match as to wavelength between the absorption properties of the material and the incident radiation. The thickness of the array is selected so as normally to absorb a large fraction of such radiation.
The efficiency of charge transport is generally thought to be a function of the arrangement of the molecules of the array; charge losses probably are associated, at least in part, with disorder. However, from the analogy of inorganic photosensitive elements, it appears that uniform ordering throughout the array does not necessarily lead to the highest possible efficiency; asymmetric arrays may be more efficient at least in some uses.
Unfortunately, known processes for assembling photosensitive arrays such as vapor deposition, crystallization, and electrolytic techniques, give little control over ordering per se. Langmuir-Blodgett films have provided ordered monolayers but the application of ordered successive layers have been without real control as to interlayer orientation. Vincett et al in Thin Solid Films 68 (1980) at p. 163 suggest the incorporation of one or more aliphatic chains into dye molecules as a means to effect desired orientation in certain Langmuir-Blodgett films to produce "organic metals" and high temperature superconductors. At p. 164 the authors suggest that the platinum atoms in complex with phenanthroline may stack to form a linear metallic chain.
As used herein `element` and `device` are essentially synonymous. The term `array` is intended to pertain to a normally ordered Photosensitive assembly of atoms or compounds. An array as here defined forms a part of an element or device. When the term array is applied to invention assemblies, it is intended further to mean an assembly comprising at least two ordered layers of metal coordination compounds, one of which may be a part of the so-called template, as will be explained infra.